Electronic computing circuit



Aug. l2, 1947. A W- VANCE ELECTRONIC COMPUTING CIRCUIT Filed Aug. 29,1942 lmsww. Mk

. Mmkumm y :h w'entl:l ARTHUR WMNCE (Ittorneg Patented ug. l2, 19472,425,405 ELECTRONIC COMPUTING CRCUIT Arthur W. Vance, Moorestown, N.J., assignor to Radio Corporation of America, a corporation of DelawareApplication August 29, 1942, Serial No. 456,590

This invention relates generally to electronic v' computers andparticularly to a circuit for providing an output voltage proportionalin amplitude to the product or quotient of two or more applied voltages,the amplitudes of which are representative of selected values of thevariables of the equation to be solved.

A thermionic tube ampliiier may be considered to be a naturalmultiplying or dividing device, since the output voltage is proportionalto the input voltage multiplied .by the gain. The gain may be made todepend on the bias applied to the control electrode circuit of the'ampliiier tube. However, in ordinary amplifiers the relation betweengain and control electrode bias is nonlinear due to individual tubecharacteristics, power supply variations, input voltage amplitude, andfrequency. It is therefore necessary to compensate for non-linearity ina variable gain amplifier 4before such a device may be utilized as ahigh accuracy electronic multiplier.

The instant invention contemplates the use of a variable gain amplifieras a multiplying device wherein the multiplicand is applied to theamplifier input as an A.C. potential of selected amplitude and, themultiplier is applied to the amplifier control electrode as a D.C. biasvoltage of selected amplitude. The product is derived from the amplifieroutput circuit as an A.C. potential having an amplitude proportional tothe product of the two applied voltages. Compensation for non-linearityof the amplifier gain is accomplished by applying to the amplifier inputcircuit an additional A.C. potential of a frequency different from thatof the first mentioned A.C. potential. The two frequencies aresegregated in the amplifier output circuit by means of suitable lternetworks, and the second, or control, A.C. potential is rectified andapplied to the amplier input through a suitable feedback circuit toprovide a compensating bias Voltage. Division of selected values of thevariables may be effected by adjusting the potential of the second A.C.potential applied to the variable gain amplifier to a value proportionalto a selected value of a variable representing the divisor.

Among the objects of the invention are to provide a novel and improvedmethod of and means for multiplying or dividing electronically two ormore variables applied to a thermionic tube circuit in terms of twovoltages of amplitude proportional to the selected values of thevariables.

Another object is to provide an improved electronic computer formultiplying two quantities of which one quantity is applied to the inputof a variable gain amplier as an A.C. potential,

and the other quantity is applied as a D.C. potential to control thegain of the amplifier. Still another object of the invention is tocompensate for non-linearity in the gain of a variable gain amplifier byutilizing a control signal, of a frequency substantially different thanthe A.C. signal which is applied as a multiplicand to the amplifierinput, for deriving through a feedback circuit a D.C. control potentialwhich is applied to the amplifier as an automatic gain control voltage.A further object of the invention is to provide an indicator for thecomputer described heretofore which will directly indicate the productof the two applied voltages which are representative of the individualquantities to be multiplied.

The invention will be described in greater detail by reference to theaccompanying drawing of which Figure 1 is a schematic block diagram ofthe invention, and Figure 2 is a schematic circuit diagram of apreferred embodiment thereof. Similar reference numerals are applied tosimilar elements throughout the drawing.

Referring to Fig. 1, a source of substantially constant amplitude A.C.potential is derived from a conventional oscillator having a frequency,for example of 25 kilocycles, and applied to the input cir-cuit of avariable gain amplifier 2. The output of a second oscillator circuit 3having a frequency, for example of l0 kilocycles, is also applied to theinput circuit of the variable gain amplifier 2. The voltage amplitude ofthe 10 kilocycle applied signal may be varied to represent a selectedvalue of one of the quantities to be multiplied. The output of thevariable gain amplifier is applied to a constant gain A.C. amplifier 4which includes a conventional inverse feedback circuit 5. The output ofthe constant gain amplifier is applied to the input of two conventionalfilter circuits 6,v 1, which are designed to pass 10 kilocycle and 25kilocycle signals, respectively.

The 25 kilocycle signal, transmitted by the 25 kilocycle filter l, isapplied to a linear rectifier 8 to derive a D.C. potential proportionalin amplitude to the 25 kilocycle control signal derived from thevariable gain amplifier. This control D.C. potential is subtracted froma second D.C. potential Vi, derived from a source 9, having an amplitudeproportional to the selected value of the second quantity to bemultiplied. The difference D.C. potential is amplified by a D.C.ampliiier l0 and applied to the variable gain amplifier 2 to control thegain thereof. The 25 kilocycle signal will therefore provide a D.C.control potential component which will compensate -lampliiien 3 forOrdinary non-linearity of the Variable gain amplifier. The D.C. voltageV1 derived from the source 9, will linearly control the gain of thevariable gain amplifier 2in accordance With the selected value of thevoltage Vi. The kilocycle signal output of the 10 kilocycle lter 6 Willtherefore have a potential substantially directly proportional to theproduct of the 10 kilocycle input potential V2 and the D.C. gain controlpotential V1 applied to the variable gain amplifier 2.

In Fig. 2, the 10 kilocycle input signal is derived from a conventionalthermionic tube oscillator I3, the output ofvvhich is applied through avariable resistor 23 to the cathode circuit of the variable gaifnamplier l2. The selected value of the first variable X is adjusted byvarying the variable resistor 23 to apply the 10 kilo-- cycle signal tothe cathode of the variablegain amplifier i2, to provide a voltage whichis proportional to the value of X. The 25 kilocycle. sig- 'nal'is alsoapplied to the cathode ofthe variable gain amplifier l2 through a secondVariable resistor ZL'Which is connected in the output circuit of thekilocycle therrnionic tube oscillator Il. I

If the`25 kilocycle signal, applied to the cathode of thevariable gainamplifier tube l2,is of just sufficient amplitude to provide thedesiredautomatic gain control bias voltage to be described hereinafter, thecircuit provides multiplication only. If, however, division .is desired,the arnl plitudeof the l0 kilocycle signal may be divided by adjustingthe amplitude of the applied 25 kilocycle signal by varying the secondvariable resistor 2l to provideaV 25 kilocycle potentialori the cathodeof the tube l2 which is proportional" in amplitude to the selecteddivisor.

A constant gain AAC. amplifier l includes the -first and second A. C.amplifier ntube lIll "and l5 and the conventional inverse feedbackcircuit 5. The loutput ofthe v,variable gain amplifier tube |2visapplied to the control electrode of the first A.C. ampliiier tube i4through any suitable coupling circuit. The output ofthe second constantgain.A.-.C. amplifier tube .l 5 is applied to the inputs ofthe l0kilocycle lterf and the 25 kilocycle filter 1.

The D.C. potential S, corresponding to the second variable Y, may bederived, in any .con-

venient manner, from a D.-.C. generator or battery, not shown. rihedesired'value of the llc-C. potential is selected by a third variableresistor i9. The selected D.C. potential corresponding .to the variableY, and the 25 kilocycleV` signal transmitted by the 25 kilocycle filter1, are applied to a linear rectiiier; tube 8, Which'inay be a pentodeoperated on the linearportion of itsjdetection characteristic, The D.C.potential, rep resentative of :the variable Y, and the 25 kilocyclecontrol potentialare effectively subtracted in the linear rectifier 8.The resultant D.C. potential is further amplied in the D.C. amplifieril), which f comprises the first and second fD.C. amplifier tubes 2liand 35. The output of the second D.-C.

' ,amplitude to the non-.linearity of the lvariable gain amplifier andassociated circuits. ,.'The 25 kilocycle component will thereforeprovide effective automatic gain controlof the variable gain irmaybe'applied to any suitable indicator l1, to

The: .output of ,the Y1,0 kilocyclegiilter K 4 indicate directly the 10kilocycle voltage output as a function of the product of the selectedvalues of the variables X and Y.

In order to assure linear detection in the pentode rectifier 8, anadditional 25 kilocycle signal is applied to the input of the firstconstant gain amplifier tube lll in order to obtain la relatively high25 kilocycle control signal Without applying the full 25 kilocyclesignal to the cathode circuit of the variable gain amplifier l2.Compensation for the additional 25 kilocycle signal is effected .by anadditional negative bias applied to the rectifier tube 8' from a batteryo-r other source I6.

The rectier tube 8 is biased by the battery I6 to operate ysubstantiallyas a linear rectifier. Naturally, such a rectier is linear only over arelatively narrow range of input voltages. Therefore, the 25 kc. levelapplied to the rectifier has y positive peaks which have values at aboutthe same level as the bias'battery IB. The actual level Vvariation ofthe`25 kc. signal is very slight sinceY such variations onlyoccurtoprovide the necessary A.V.-C. control and the high loop gain of the'system due to thearnplifiers land I'Urerquires only a small `signal atthe grid ofthe rectifier tube 8.' Also due to thevrelatively'highjgainof the D.C. amplifier lil, the levelof the 4DAC. voltage representingthe variable vY is at allow value as applied to the grid oftherectifier; Any non-linearity in the rectifier and in the amplifieriii is'cornpensated by the A.V.C. control provided by the 25 kc.feedback signal.'l l

A multiplying circuit of the type described can theoretically be madeto'provide vany degree of precision over Aany reasonable krang-e, v'ifsugiciently high voltages land power are. available. From apracticalsta-ndpoint, a `relativelysimple multiplier, of the general vtypedescribed, I nayjibe vbuilt tohave arange of one to oney thousand in theinput and outputpotentials, .with anaccuracy yof the order rof one partin tenthousand. 1 The operating timenecessary for therriultiplicationmustbe larger'than the period of the lowest'applied frequency.` The`multiplication time'may therefore be considerablyV reduced'b-yincreasing the input frequencies.

Thus the invention described ."co'rnprisesan electronic computer, fornfnlltiplying.tvvofquarti-V tities, in which the quantities Vare appliedrespectively Ias AJC. and D.O. potentials to-'agvariable gain amplifier,whereby the D.,C. potential controls the vgain,'and therefore theoutput,pq--

tential of vthe A.fCQinput, and the output `nuff).

v potential may be applied to the indicatorjtoindicate directly theproduct of the twoquantities.

A second A.C. input signaLnof ajdifferentffrequency than the 'firstVmentioned vifl.. -Cj. input, s

utilized to Hcorn-pensate` for non-,linearintyl'in "the Y gain. of`thevariable gaingarnplifier by applying va controlloias through avfeedback circuitljj n 1 j 'Division .of the quantity represented. v'byfthe applied 10 kilocvcle;potentalmay'beieiegtei'by varying theamplitude ,of .the yapplied 25 jlilocycle potential Yto,the cal'fl'iodeof the variablegafllampimer. Thek pctentiaiefthe iiiiocyciesignai thusapplied should .beA proportional tothe selected value ofV 'the divisor.Vin otlgier vlorldsgthe setting of the control 23 determinesjthe valueYof Vthe dividend, thesetting of "the contro-l 2 l jgleter ininesthevalue ofA the divisor, andthe s ,of the D.C'. control lgjdeterm'inesthese ,Y

Therefore, the equation ,A Y,

may be solved in one operation, where a, b, and c are separate Variablesand n: is the resultant.

I claim as my invention:

1. The combination of a variable gain amplier having a cathode and acontrol grid, means for applying to said cathode first and secondalternating potentials having different frequencies, a constant gainamplifier for amplifying the output of said variable gain amplifier,means connected to the output of said constant gain amplifier forsegregating the second of said alternat- -ing potentials, meansproviding a unidirectional potential, means including a linear rectifierfor providing a control potential proportional to the difference betweensaid segregated and unidirect-ional potentials, means for applying saidcontrol -potential to said control grid, and means for` deriving fromthe output of said constant gain amplifier an alternating potentialwhich has the same frequency as that of said first alternating potentialand has an amplitude proportional to the product of the amplitudes ofsaid unidirectional and first alternating potentials.

2. The combination of a variable gain amplifier having a cathode and acontrol grid, means for applying to said cathode rst and secondalternating potentials having different frequencies, a constant gainamplifier for amplifying the output of said Variable gain amplifier,means connected to the output of said constant gain amplifier forsegregating the second of said alternating potentials, means providing aunidirectional potential, means including a linear rectifier forproviding a control potential proportional to the difference betweensaid segregated and unidirectional potentials, means for applying saidcontrol potential to said control grid, and means for deriving from theoutput of said constant gain amplifier an alternating potential whichhas the same frequency as that of said first alternating potential andhas an amplitude proportional to the product of the amplitudes of saidunidirectional and first alternating potentials, divided by theamplitude of said second alternating potential.

3. The combination of a variable gain amplifier having a cathode and acontrol grid, means for applying to said cathode first and secondalternating potentials having different frequencies, a constant gainamplifier for amplifying the output of said variable gain amplifier,means connected to the output of said constant gain amplifier forsegregating the second of said alternating potentials, means providing aunidirectional potential, means including a linear rectifier forproviding a control potential proportional to the difference betweensaid segregated and unidirectional potentials, means for applying saidcontrol potential to said control grid, and means for deriving from theoutput of said constant gain amplifier an alternating potential whichhas the same frequency as that of said first alternating potential andhas an amplitude proportional to the product of the amplitudes of saidunidirectional and rst alternating potentials, means for adjusting theamplitude of said first alternating potential to represent differentvalues of a first variable, and means for adjusting said unidirectionalpotential to represent different values of a second variable.

4. The combination of a variable gain amplifier having a cathode and acontrol grid, means for applying to said cathode first and secondalternating potentials having different frequencies, a constant gainamplifier for amplifying the output of said Variable gain amplifier,means connected to the output of said constant gain amplifier forsegregating the second of said alternating potentials, means providing aunidirectional potential, means including a linear rectifier forproviding a control potential proportional to the difference betweensaid segregated and unidirectional potentials, means for applying saidcontrol potential to said control grid, and means for deriving from theoutput of said constant gain amplifier an alternating potential whichhas the same frequency as that of said first alternating potential andhas an amplitude proportional to the product of the amplitudes of saidunidirectional and first alternating potentials, divided by theamplitude of said second alternating potential, and means for adjustingthe amplitudes of said first and second alternating potentials and thevalue of said unidirectional potential to represent respectivelydifferent Values of three different variables.

ARTHUR W. VANCE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,869,209 Mead, Jr i July 26,1932 2,100,375 Blair Nov. 30, 1937 2,111,607 Black Mar. 22, 19382,178,333 Blair Oct. 31, 1939 2,179,915 Blair Nov. 14, 1939

